This invention relates to a one-way valve and in particular to a one-way valve suitable for flexibly walled packages. Such flexibly walled packages are used extensively for packaging food stuffs such as roasted coffee beans, grounds, and the like.
In the past, one-way valves have been used for preventing the exposure of packaged food stuffs to the effects of oxygen. Oxygen in the presence of many foods promotes an oxidation reaction which can result in the food loosing its flavour, texture or colour. Consequently, it is advantageous to the saleability of the food to prevent the food from coming into contact with oxygen. In the case of roasted coffee, there is the additional factor that the roasted coffee tends to produce gas over a period of time after being contained in the flexible packaging. The production of such gas must be accommodated, either by an expanding flexible container or more simply by a one-way valve which permits the egress of gases produced by the roasted coffee while prohibiting any ingress of air containing oxygen and the like.
Roasted coffee tends to produce CO.sub.2 over time. The rate of gas emission depends upon such factors such as bean origin, roast and storage temperature, grind size, surrounding atmospheric pressure and the length of time since the coffee was roasted. Typically, greater amounts of gas are given off immediately after roasting The emission rate can also be influenced by evacuating or flushing a container of freshly roasted coffee with an inert gas. Because the amount of gas is variable, a one way valve is preferred over a flexible package. In a flexible package, an overpressure is likely to burst the package rendering the goods unsaleable. A one way valve, on the other hand will allow overpressure inside of the package to vent, thus maintaining a safe pressure at all times. The valve also has the advantage that the initial gas produced will tend to displace any air, and oxygen, which becomes trapped in the package during packaging. With a one way valve, flushing or purging of the package to eliminate such trapped air may be unnecessary.
Valves have been known, and an example of such a valve is illustrated in Canadian Pat. No. 1,177,449 entitled OVERPRESSURE VALVE FOR PACKAGES WITH FLEXIBLE WALLS which issued on Nov. 6, 1984 in the name of Wipf AG Verpackungen. In this patent a one-way valve is disclosed which essentially comprises a valve body in which seats a circular imperforate valve diaphragm in a disk-like depression. A keeper is inserted into the depression and prevents the diaphragm from being removed from the valve seat. The keeper is retained under a lip formed on the sides of the disk-like depression.
However, this Wipf device has several disadvantages. Firstly, the device requires that the keeper be inserted into the valve body after the diaphragm has been put in place. Having a valve body which is essentially of two piece construction, namely, the keeper, and the valve body with the disk like depression, is expensive and labour intensive to assemble. Secondly, in the installed position, the keeper is exposed to the outside of the package. Therefore, the keeper may be accidentally or purposely removed thereby disrupting the ability of the valve to function as intended. This is clearly unacceptable and it would be preferable if the valve was kept safely out of sight. A further disadvantage with this device is that there is no disclosure of a filter or the like to prevent fine dust or other bits of the food stuffs from entering into the valve opening and being lodged between the diaphragm and the valve seat. Such a situation would impair the ability of the valve seat to prevent the ingress of oxygen air or the like into the package. Yet a further problem with this device is that when the valve diaphram ceases to function, for any reason, there is no provision for any back-up to at least ensure a minimum level of functioning of the valve.
What is desired is a unitary valve body that is simple to manufacture and easy to install. What is also desired is a valve body which can be secured to a package in a manner that the operational elements of the valve are not exposed externally. A further aspect that is desirable is that a gas produced inside the package be filtered to prevent the valve seat from being contaminated. It would also be preferrable to provide a valve having a second sealing action, which could act as a safety measure.